Firearms are typically aimed by aligning a front sight with a rear sight. A typical front sight includes a post or bead, which is aligned within a U-shaped notch, V-shaped notch, or aperture that is included within a rear sight. By centering the front sight or portion thereof within the rear sight, and aligning the top of the front sight with the target, the firearm may be accurately aimed at the target.
The sights are typically located a short distance from the center of the barrel, so that aligning the sights exactly parallel with the barrel will result in the bullet striking the target below the point of aim, a concept known as parallax. Furthermore, the bullet will drop during flight, producing a curved trajectory. Therefore, it is generally desirable for the sights to be aligned at a slight angle to the barrel, so that perfect horizontal sight alignment will result in a slight upward angle of the barrel. Ideally, this will cause the bullet to pass through the axis of the sights at two distances, first as it is rising, and second as it is falling. The distances at which this occurs can be adjusted by adjusting the position of the sights relative to each other.
The relationship between the point of impact indicated by sight alignment and the actual point of impact of the bullet on the target can be adjusted according to well-known principles. For example, if a shooter desires to move the point of impact of bullets on the target to the right, this can be achieved by moving the rear sight to the right, or the front sight to the left. Similarly, moving the rear sight to the left, or the front sight to the right, will move the point of impact of bullets on the target to the left. Raising the height of the rear sight, or lowering the height of the front sight, will raise the point of impact of bullets on the target. Similarly, lowering the height of the rear sight, or raising the height of the front sight, will lower the point of impact of bullets on the target. Using these well-known principles, a shooter may adjust the position of one or both sights to bring the point of impact of bullets on the target to the point indicated by proper alignment of the sights at a given distance. Additionally, small differences in the manner in which different shooters perceive sight alignment may be present. These small differences, when magnified by the distance to the target, can become significant. Therefore, adjustment of the sights is helpful in ensuring that a given shooter's perception of proper sight alignment results in the proper point of impact on the target.
The means of adjusting sights as described above depends on the type of sights. Sights which are completely fixed must typically be adjusted by filing, or in the case of a revolver, by rotating the barrel to move the front sight. Obviously, completely fixed sights not only make adjustment difficult, but also make replacement of the sights with a different style of sights difficult. Many sights for semi automatic handguns are presently mounted within transverse dovetail cuts defined within the slide, held in place by an interference fit and/or by set screws. These sights can be adjusted for horizontal alignment by moving the sights within the dovetail channels. Vertical adjustment requires either filing or replacement of one or both sights with sights of different heights. The dovetail cuts are not cosmetically optimal, and provide no assistance in centering the sights on the firearm, which is often the optimal position for horizontal alignment. Additionally, installation of sights in dovetail cuts usually requires the use of specialized tools, which may not be in the possession of the shooter. Furthermore, dovetail mounted sights have been known to work loose over time. In particular, repeated removals and installations can loosen an interference fit. Nonetheless, dovetail cuts are popular because they facilitate sight replacement and some horizontal sight adjustment.
Many presently available sights include a means for adjusting the position of the front and/or rear sight relative to the other sight. These sights will often use a screw to bias a portion of the sight in one direction, and a spring to bias the portion of the sight in another direction. One such mechanism is used to control vertical adjustment, and a similar mechanism is utilized to control horizontal adjustment. Often, these sights require cutouts in the slide or other firearm components that specifically accommodate those sights, thereby making it very difficult to replace the sights with a different style of sight. An example is the Elliason style sight that was utilized on some past examples of 1911 style pictures manufactured by Colt. Given the popularity of dovetail cuts, some adjustable sights have been designed to fit standard dovetail cuts, and therefore carry the cosmetic and centering disadvantages inherent in dovetail cuts.
Demands are often placed on firearm sights beyond their use in aiming a firearm. For example, in the case of a semi automatic handgun, a shooter with an injury to one arm may have a need to manipulate the handgun using only one hand. Many training exercises mimic this need. Retracting the slide, as would be necessary for reloading and/or clearing malfunctions, is often accomplished by hooking the rear sight onto a belt, the heel of a shoe, or other convenient surface. The rear sight must therefore be able to withstand the stresses of being used to retract the slide.
Accordingly, there is a need for a firearm sight that is easily installed and/or replaced by the shooter, preferably without tools. Towards this end, there is a need for a firearm sight having a design that provides for automatic centering of the sight on the firearm. There is a further need for a firearm sight that is easily replaceable with other styles of firearm sights. Additionally, there is a need for a firearm sight that provides adjustability without the need for specialized cutouts. Furthermore, there is a need for a firearm sight that avoids the cosmetic disadvantages of previous firearm sights. There is an additional need for a firearm sight that has sufficient strength for use in retracting the slide of a semi automatic handgun.